Layers crosslinkable by light

ABSTRACT

Soluble polymeric cyclopentadienes form particularly desirable light-sensitive layers, being crosslinked to insoluble condition by light with or without the help of a crosslinking agent.

United StiltGS Patent 1 Kolb et al.

[4s] Feb. 27, 1973 LAYERS CROSSLINKABLE BY LIGHT [75] Inventors: GunterKolb; Adolf Schmidt; Robert Schmitz-Josten; Erich Wolff, all ofLeverkusen, Germany [73] Assignee: Agia-Gevaert Aktiengesellschait,

Leverkusen, Germany 221 Filed: April 5, 1971 21 Appl.N0.: 131,526

[30] Foreign Application Priority Data April 23, 1970 Germany ..P 20 19598.6

[56] References Cited UNITED STATES PATENTS 2,463,596 3/1949 Butlers.....260/93.1 3,467,523 9/1969 Seidel et a1. ..96/91 N FOREIGN PATENTS ORAPPLICATIONS 767,985 2/1957 Great Britain ..96/91 N PrimaryExaminer-Alfred L. Leavitt Assistant Examiner-John H. NewsomeAttorney-Connolly and Hum [5 7] ABSTRACT Soluble polymericcyclopentadienes form particularly desirable light-sensitive layers,being crosslinked to insoluble condition by light with or without thehelp of a crosslinking agent.

5 Claims, No Drawings LAYERS CROSSLTNKABLE BY LIGHT The presentinvention relates to light-sensitive layers containing polymers havingcyclopentene rings, which can be crosslinked by light.

Light-sensitive polymers are known, which are crosslinked at the exposedareas, i.e., they are hardened so as to produce an image. When they aresubsequently developed with a solvent which is suitable for theparticular polymer, the non-light-struck areas of the layer which havenot been crosslinked can be dissolved away, while the exposedcrosslinked image parts of the layer are insoluble forming a reliefimage on the layer support.

Layers of this kind generally contain photocrosslinking agents such asbichromates, azides or cinnamic acid esters. These crosslinking groupsmay either be combined with the polymer itself or added to the layer inthe form of a separate crosslinking agent. Suitable layers containcyclorubber or condensation products of epichlorohydrin and2,2-bis-(4-hydroxy-phenyl)- propane as polymers and diaryl azides ascrosslinking agents. It is also known to use aromatic carbonyl azidecompounds or sulfonyl azide compounds as crosslinking agents.

The known light-sensitive layers have, however, certain disadvantages,for example the sensitivity to light is generally insufficient so thatrelatively long exposure times are necessary to obtain sufficientlysharp relief images. Other polymers, e.g., those which have beencrosslinked with cinnamic acid derivatives, are insufficiently resistantto strong acids so that they cannot be used for the production of imagesby etching foils of noble metals. Various polymers are sufficiently acidresistant but not sufficiently heat resistant so that they becomeunusable in the course of storage because they undergo slow thermalcrosslinking even without exposure. Other polymers are very highly acidresistant and sufficiently heat resistant but the removal of theunexposed parts of the layer requires the use of solvents in which eventhe crosslinked parts undergo severe swelling, so that the relief imagesobtained are not sharp.

It is among the object of the present invention to provide layers whichcan be crosslinked by light and which have improved sensitivity to lightand improved resistance to chemicals and especially to acids.

We now have found a light-sensitive layer which contains a polymercapable of being crosslinked upon exposure in the presence oflight-sensitive crosslinking agents, wherein the crosslinkable polymeris a homopolymer or copolymer of cyclopentadiene or derivatives thereof.

Especially advantageous are those polymers in which the cyclopentenering which is formed by the polymerization of cyclopentadiene is in thel,2--or 1,3- position within the polymer chain in the form of structuralelements of the following formulas:

a R R a R a R or R R n wherein R stands for hydrogen or alkyl havingpreferably one to five carbon atoms; polymers in which at least one R inl-position to the double band represents hydrogen are As alreadymentioned above, homopolymers ofcyclopentadiene or its substitutionproducts or copolymers of these cyclopentadienes with each other or withother comonomers are suitable for the lightsensitive layers. Theadditional comonomers used may be practically any compounds which arecopolymerizable with cyclopentadienes, for example: olefines such asisobutylene, butadiene, isoprene or 2,3-dimethylbutadiene; styrene orits derivatives, such as substitution products with are alkylated on thebenzene ring, especially with alkyl having up to three carbon atoms, orhalogenated substitution products, e.g., products which are substitutedwith chlorine or bromine, or nitrated or alkoxylated substitutionproducts; styrenes which are substituted on the ethylene group, such asa-methyl styrene, these derivatives may also be substituted on thebenzene ring; substituted or unsubstituted indene and substituted orunsubstituted acenaphthylene.

The homopolymers or copolymers to be used according to the invention maybe prepared by known methods, e.g., with the aid of cationic initiatorsof the Friedel-Crafts type and preferably with boron halides oraluminium halides or their complex compounds with ethers, alcohols andorganic acids, especially halogenated carboxylic acids such as mono-,dior trichloroacetic acid, or with complex compounds consisting of 1 molof triphenylmethyl chloride and 1 mol of boron halide or aluminiumhalide, at temperatures of between about 100 C and +50 C. Polymerizationmay be carried out continuously or discontinuously in solution or inbulk, About 0.3 to 2.5 parts of catalyst are used for 100 parts ofmonomer mixture. The polymerization temperature employed is preferablybetween about C and 10 C.

If polymerization is carried out in solution, the solvents used may ben-alkanes, cycloaliphatic conipounds having more than five carbon atomsin the ring, aromatic hydrocarbons such as benzene, toluene or xylene orhalogenated hydrocarbons such as methylene chloride, chloroform or1,1-dichloroethane. If this polymerization has been inducedcationically, the molecular weight of the products obtained generallyincrease with the polarity of the reaction medium, i.e., the moresolvent with a high dielectric constant is present in the mixture, thehigher is the molecular weight obtained. Instead of purely polar ornon-polar solvents, solvent mixtures of polar and non-polar componentsmay also be used.

Solvent combinations of polar halogenated hydrocarbons (such asmethylene chloride or 1,2- dichloroethane) with aromatic hydrocarbons,n-alkanes or cycloalkanes (such as toluene, n-hexane or cyclohexane) arefound to be especially suitable reaction media for the preparation ofhigh molecular weight soluble homopolymers and copolymers ofcyclopentadiene.

The molecular weight of the homopolymers or copolymers can be affectednot only by the choice of suitable solvents, but, of course, also by thepolymerization temperature, low temperatures leading to the formation ofhigher molecular weight products.

It is therefore possible to obtain high yields of homopolymers andcopolymers of cyclopentadiene having viscosity numbers ranging from [1;]0.1 to [1 3 depending on the solvents and polymerization temperatures.The preparation of polycyclopentadienes having viscosity numbers of 0.4to 2.0 is described i Macromol. Chem. (1969) 90-102.

The preparation of a few copolymers is described in detail below. Othersare obtained by similar methods. Copolymers of Cyclopentadiene anda-Methyl Styrene 1. 0.3 g of an addition product of BF and anisoledissolved in 100 cc of toluene is added dropwise at various temperaturesto a mixture of 25 g of cyclopentadiene and 25 g of a-methyl styrene in250 g of toluene which contains about 30 ppm of water. Copolymers whoseintrinsic viscosity varies with the polymerization temperature as shownbelow are obtained in almost quantitative yields.

Temperature: C C 45 C 78 C [1 25 C, toluene 0.2-0.3 0.3-0.6 0.6-0.80.8-1.1

The copolymerization parameters are r 1.6 (cyclopentadiene) and r 0.8(oz-methyl styrene).

On fractionating a copolymer having a viscosity of [n] 0.73, it wasfound that cyclopentadiene copolymerizes very regularly with a-methylstyrene as indicated below.

Mol of a-methyl styrene Fraction by weight [11] in the copolymer 1 11.31.63 31 2 14.1 1.20 32.8 3 10.0 0.93 34.1 36 4 14.0 0.78 35 S 16.8 0.5937 X1 6 10.16 0.46 38.2% 7 10.2 0.28 39 Products which are even moreuniform in composition can be obtained by varying the rates at which themonomers are added according to the different reactivities of themonomers.

The viscosity numbers of the copolymers also depend on the total monomerconcentration c at the start of the polymerization and on thecomposition of the monomer mixture. The viscosity numbers of thecopolymers increase with increasing cyclopentadiene content and highervalues are obtained for [1)] than indicated above.

If polymerization is carried out in m-xylene under the same conditions,the copolymers obtained have substantially lower molecular weights. Evenproducts so prepared at 80 C never have viscosity numbers above [1;]=0.6.

2. 0.4 g of boron fluoride diacetic acid (BF,'2 CH,COOH) dissolved in 50ml of chloroform is added dropwise in the course of 10 minutes to asolution, which has been cooled to 70 C, of 50 g of cyclopentadiene and50 g of a-methyl styrene in 400 cc of chloroform (anhydrous).Polymerization is completed after 30 minutes. 98 g of a high molecularweight, soluble, gel-free copolymer which has an intrinsic viscosity of[1;] 1.5 are obtained.

If instead of BP -acetic acid, the addition product of BF,, and diethylether is used under otherwise the same conditions, copolymers havingviscosity numbers of about [1,] 2 are obtained in yields of 60 topercent.

If 1,2-dichloroethane is used as the solvent instead of chloroform andBF -diethyl ether is used as catalyst and the polymerization conditionsare otherwise kept the same, soluble copolymers which have not beencrosslinked and which have viscosity numbers of [1;] 3.0 to 3.5 areobtained in yields of 40 to 50 percent. Copolymer of Cyclopentadiene andp-Methyl-a- Methyl styrene A mixture of 32.5 g of p-methyl-a-methylstyrene and 17.5 g of cyclopentadiene in 290 g of toluene is cooled to78 C. A solution of 1.0 g of BF -anisole in 50 cc of toluene is addeddropwise in the course of 10 minutes. The temperature rises to 60" C. 50g of a copolymer which has a viscosity of [1 0.75 are obtained.

Copolymer of Cyclopentadiene and p-Chloro-a-Methyl Styrene A mixture of40 g of p-chloro-a-methyl styrene and 20 g of cyclopentadiene dissolvedin 300 g of toluene is cooled to 78 C. A solution of 1.0 g of BFtrichloroethanol is added dropwise in the course of 10 minutes. Thetemperature rises up to 5 0 C. 55 to 60 g of a copolymer which has aviscositynumber of [1;] 0.8 to 0.9 are obtained.

Copolymer of Cyclopentadiene and lndene Fifty g of indene and 50 g ofcyclopentadiene are dissolved in 283 g of toluene, and a'solution of 2 gof B1 anisole adduct dissolved in 100 cc of toluene is added dropwise inthe course of 50 minutes. The temperature is maintained at 78 C. Acopolymer having viscosity numbers of [1 =0.6 to 0.8 is obtained.

Copolymer of Cyclopentadiene with lsobutylene and a- Methyl Styrene Amixture of 35 g of cyclopentadiene, 35 g of isobutylene and 35 g ofa-methyl styrene is dissolved in 400 cc of methylene chloride, and asolution of 1.4 g of trichloroethanol-BF, adduct dissolved in 100 cc ofmethylene chloride is added dropwise at 70 C. g of a copolymer which hasa viscosity number of [1;] 0.3 to 0.4 are obtained.

Copolymer of Cyclopentadiene and Acenaphthylene Seventeen g ofcyclopentadiene and 8 g of acenaphthylene are dissolved in 145 g oftoluene. A solution of 0.25 g of BF -anisole dissolved in ml of tolueneis added dropwise at 78 C in the course of 20 minutes. The copolymer,which is obtained in 80 percent yield, has viscosity numbers of [1;] 0.7to 0.8. Copolymer of 1,3-Dimethylcyclopentadiene and a- Methyl StyreneForty g of 1,3-dimethylcyclopentadiene and 20 g of a-rnethyl styrene aredissolved in 250 cc of toluene and the mixture is cooled to 78 C. 1.5 gof BF -anisole dissolved in 100 cc of toluene are now added dropwise.The temperature rises to about 40 C. A soluble copolymer (viscositynumbers [1;] 0.7 to 1.0) is obtained in quantitative yield.

Layers which can be crosslinked by light and which have excellentmechanical properties, excellent sensitivity to light and surprisinglyhighacid resistance are obtained by means of the homopolymers orcopolymers described above. Copolymers of cyclopentadienes with othercomonomers are especially suitable owing to their superior stability instorage compared with that of homopolymers.

The molar ratio of cyclopentadiene and comonomers may vary within sidelimits. The general rule applies that the higher the molar concentrationof a cyclopentadiene in the polymer, the greater is the lightsensitivity of the layers. Layers which can be crosslinked by light cantherefore be produced with the required sensitivity to light accordingto the requirements of the particular reproduction process for which thelight-sensitive layer is to be used.

Comonomers which contain the cyclopentadiene component at a molarconcentration of between 30 and 70 mols per cent are preferred for manydifferent requirements.

The molecular weight of the polymers used according to the invention mayalso vary within wide limits. Molecular weights ranging between 5,000and 1,500,000 have generally been found suitable. The choice of polymershaving a suitable molecular weight generally depends on the purpose forwhich they are to be used, i.e., the requirements of the particularreproduction process. In general, higher molecular weight polymers areespecially suitable in cases where only short exposure times arepossible, i.e., where highly sensitive light-crosslinkable layers arerequired. It is therefore also possible to prepare polymers which havethe required sensitivity by suitable choice of the molecular weight. Themolecular weight range indicated above corresponds to viscosity numbers(intrinsic viscosity) of [n] 0.4 to 1.8.

The layers according to the invention which can be crosslinked by lighthave such a high sensitivity to light that the use of specialcrosslinking agents is not necessary. In many cases, however, it isadvantageous to modify the properties of the layers by using separatelight-sensitive crosslinking agents.

Suitable for this purpose are, for example, lowmolecular organic azidecompounds, especially aromatic compounds which contain azide, carbonylazide, sulfonyl azide or azido formate groups. Compounds of this typehave been described, for example, in German Pat. Nos. 954,308; 1,079,950and 1,285,306 and in British Pat. No. 767,985. The optimum combinationsof crosslinking agents and polymers which can be crosslinked can easilybe determined by a few simple commonly used laboratory tests.

Low molecular weight preferably low molecular weight benzene azidocompounds which contain at least two azide groups are suitable for useas crosslinking agents. The following are mentioned as examples:

4,4'-diazido stilbene 1,4-diazido benzene 4,4'-diazido benzophenone4,4'-diazido diphenylmethane 4,4'-diazido dibenzal acetonel,3-di-(40'-azidophenyl)-2,3-propen-l-onel,2-di-(4-azidocinnamoyloxy)-ethane 4,4-diazido dibenzal cyclohexanone,and

2,6-di-(4-azido benzal)-4-methylcyclohexanone;

furthermore, sulfazides, e.g., l,4-butane disulfazide, and especially1,3-benzene disulfazide and derivatives thereof such astoluene-2,4-disulfazide or 4-amino-6 chloro-m-benzene disulfazides;sulfazides which contain two phenyl groups may also be used, inparticular 4,4'-diphenyl disulfazide, 4,4'-diphenyl ether disulfazideand especially methylene-bis-(4-phenylene sulfazide),4,4'-dichlorodiphenyl-2,6'-disulfazide or 4,4-dichlorodiphenyl-3,5-disulfazide; naphthalene disulfazides are alsoespecially suitable, e.g., 1,5-naphthylene disulfazide, 2,6-naphthylenedisulfazide or 2,7- naphthylene disulfazide.

The concentration of crosslinking agent in the layer of film-formingpolymers may vary within wide limits according to the nature of thecomponents in this system and the required results. Concentrations ofabout 0.5 to 25 percent by weight of the azido crosslinking agent in thelayer are sufficient for the usual purposes. The optimum concentrationfor any particular case can be determined by a few simple tests. Itdepends primarily on the nature and molecular weight of the polymer, thechemical nature of the crosslinking agent and especially on the requiredthickness of the layer.

The light sensitivity of the layers according to the invention can beconsiderably increased by the addition of sensitizers of the typenormally used for this purpose, e.g., Michlers ketone, dimethylaminobenzaldehyde, 4-H-quinolizin-4-one, compounds from the group ofnaphthothiazolines, cyanines, triphenylmethane dyes or the compoundsdescribed in French Pat. No. 1,513,822, British Pat. No. 1,148,636 andBelgian Pat. No. 735,896.

The layers produced according to the invention are exposed with theusual sources of light used in reproduction work, such as carbon arclamps, 'Xenon lamps and high pressure mercury vapor lamps. These sourcesof light advantageously contain a proportion of ultraviolet light whichis especially effective for photocrosslinking, in addition to visiblelight. Development of the exposed layers is generally carried out withorganic solvents of suitable constitution which may but need notnecessarily be the same as or similar to the solvents used for thepolymers before they have been crosslinked. Solvents such as butylacetone, cyclohexanone, benzene, xylene, glycol ethers, glycol acetatesor butanones, in which the crosslinked parts of the layer undergo littleor no swelling, are preferably used.

The light-sensitive polymers according to the invention may be presentin the layer either alone or as a physical mixture with other polymers.A mixture in many cases affords certain advantages because it ispossible to prepare mixtures which have certain advantageous propertiessuch as solubility in various solvents, improved bonding on speciallayer supports, etc. When choosing suitable components for the mixture,care must naturally be taken to ensure that they are compatible with thecyclopentadiene polymer, and in particular no separation of thecomponents must occur on formation of the film.

Especially suitable components for the mixtures are homopolymers orcopolymers of vinyl acetate, ethylene, derivatives of acrylic ormethacrylic acid such as acrylic acid amide or methacrylic acid amide,esters of these acids, especially esters with short chained aliphaticalcohols, or nitriles of these acids, or

butadiene, isoprene, styrene or vinyl alcohol. As specific examplesthere may be mentioned copolymers of vinyl acetate, vinyl alcohol,ethylene and norbornadiene and copolymers of butadiene or isoprene withstyrene and/or acrylonitrile. Mixtures with polymers which are notsensitive to light also have the advantage that unwanted prematurecrosslinking of the light-sensitive polymers during preparation of thelayer can be practically completely suppressed.

The layers which can be crosslinked by light are prepared by dissolvingthe polymers and adding the crosslinking agent to the solution. Thecrosslinking agent may be in the form of a solution or in aheterogeneously distributed form. The solution is then applied to therequired layer support in the usual manner and the solvent isevaporated. With suitable choice of layer binders, it is also possibleto produce self-supporting layers.

The layer supports may be metal foils of copper, aluminium, zinc,magnesium, steel and the like, paper, glass or foils of polymer productssuch as cellulose esters, polyvinyl acetate, polystyrene andpolycarbonates, especially those based on bis-phenylol alkanes,polyesters, especially those based on polyethylene terephthalate, andpolyamides such as nylon and the like. Materials which have a mesh-likestructure such as metal meshes are also suitable for use as supports.

The layers according to the invention which can be crosslinked by lightmay be used for the production of relief images or for printing formsfor relief printing, intaglio printing or planographic printing. Theymay be used for the offset printing process, screen printing,lithographic printing plates or any other printing processes whichrequire a relief image and photogravure processes. One importantapplication of the layers according to the invention is the productionof so-called printed circuits.

The thickness of the layer which can be crosslinked by light may varywithin wide limits. Thicknesses of between 0.001 and about 0.7 mm aresufficient for the usual processes. Thicker layers of about 0.25 to 1.5mm may be used for relief printing forms.

EXAMPLE 1 Light-Sensitive Material The following copolymers ofcyclopentadiene and amethyl styrene are prepared by the first processindicated above:

Proportion by The polymers are dissolved in xylene, and 2 percent byweight of 4,4-diazido-dibenzal cyclohexanone, based on the weight offilm-forming polymer, are added as crosslinking agent. These solutionsare whirl-coated (200 revs/min) on aluminium foils and dried. ProcessingThe various samples are exposed in close contact in a vacuum framethrough a grey step wedge having a density difference of 0.15 betweenthe individual steps. The layers are then developed in xylene for 2minutes. The results are summarized in the table below.

Steps Layer Thickness Exposure Density Polymer in microns time (min.)0.15 1 2.25 1 7 2 3.20 1 8 3 2.75 l 7 4 2.95 4 4 5 1.25 4 7 6 1.25 4 8 78.35 4 13 Sharp positive relief images of the step wedge are obtained.The relief images have excellent resistance to the etching agentsnormally used on aluminium supports, e.g., strongly alkaline aqueousbaths. Similar results are obtained when the aluminium foils arereplaced by copper. In this case, etching may be carried out, e.g., withaqueous solutions of ammonium persulphate, hydrogen peroxide or iron(Ill) chloride.

EXAMPLE 2 Light-Sensitive Material Copolymers of cyclopentadiene andindene are also prepared by the process described above. The polymersare described in the table below.

Proportion by weight (indene: Polymerization cyclopentatemperaturePolymer diene) in C. [1;] 1 30 78 0.7 2 80 z 20 78 0.8 3 70 30 40 0.4

Sample Exposure time (min) Steps Density 0.15 l 10 2 4 9 3 4 9 EXAMPLE 3Light-Sensitive Layer Two percent by weight of 4,4-diazido-dibenzalcyclohexanone, based on the weight of dry film-forming polymer, areadded to a 5.0 percent solution of polycyclopentadiene (viscosity number'1 0.80, molecular weight 150,000). A thin copper foil is coated withthis solution and the layer is dried for 5 minutes in a drying cupboardat 80 C. The resulting thickness of the layer is between 2 and 4microns. Processing The layer described above is exposed for 4 minutesthrough a grey wedge (density steps 0.15) and then developed in amixture of xylene and mineral spirits (development time 2 minutes).After washing the developed layer with water and blowing it dry withcompressed air, a sharp positive relief image of the step wedge isobtained. Sensitivity 14 steps.

EXAMPLE 4 Light-Sensitive Material 5.0 g of polycyclopentadiene(viscosity number 11 0.80, molecular weight 150,000) and 3.0 g ofpolystyrene (molecular weight 200,000) are dissolved in 200 g of tolueneand sensitized with 2 percent by weight, based on the weight of dryfilm-forming polymer, of 4,4-diazidodibenzal cyclohexanone. A thincopper foil is coated with this solution and the layer is dried in adrying cupboard at 80 C. The resulting thickness of the layer is between2 and 4 microns. Processing The layer described above is exposed for 4minutes in a Chem-Cut vacuum frame through a grey wedge (density steps0.15) and then developed for 2 minutes in a mixture of xylene andmineral spirits. When the developed layer has been washed with water andblown dry with compressed air, a sharp relief image of the step wedge isobtained. Sensitivity: 12 steps.

We claim:

1. In an exposure assembly for imagewise exposing a layer of a solidsoluble polymer that becomes crosslinked to insoluble condition wherelight struck, the improvement according to which the soluble polymer isa cyclopentadiene polymer having recurring units of the formulas:

R R R I l R R 2;: R R-- 0, )4

- R R R wherein R stands for hydrogen or alkyl having up to five carbonatoms, and having a molecular weight between about 5 ,000 and 1,500,000.

2 The combination of claim 1 in which the polymer is a polymer ofcyclopentadiene, methyl-cyclopentadiene or dimethyl-cyclopentadiene.

3. The combination of claim 1 in which the layer also contains aslight-sensitive crosslinking agent a low molecular weight benzene azidocompound containing at least two azide groups.

4. In an exposure assembly for imagewise exposing a layer of a solidsoluble copolymer that becomes crosslinked to insoluble condition wherelight struck, the improvement according to which the soluble copolymerhas a molecular weight of about 5,000 to 1,500,000, is a copolymer ofcyclopentadiene with a styrene, and contains about 30 to mol percent ofcyclopentadiene.

5. In an exposure assembly for imagewise exposing a layer of a solidsolution copolymer that becomes crosslinked to insoluble condition wherelight struck, the improvement according to which the soluble copolymerhas a molecular weight of about 5,000 to 1,500,000, is a copolymer ofcyclopentadiene with mdene or acenaphthylene, and contains about 30 to70 mol percent of cyclopentadiene.

2. The combination of claim 1 in which the polymer is a polymer ofcyclopentadiene, methyl-cyclopentadiene or dimethyl-cyclopentadiene. 3.The combination of claim 1 in which the layer also contains aslight-sensitive crosslinking agent a low molecular weight benzene azidocompound containing at least two azide groups.
 4. In an exposureassembly for imagewise exposing a layer of a solid soluble copolymerthat becomes crosslinked to insoluble condition where light struck, theimprovement according to which the soluble copolymer has a molecularweight of about 5,000 to 1, 500,000, is a copolymer of cyclopentadienewith a styrene, and contains about 30 to 70 mol percent ofcyclopentadiene.
 5. In an exposure assembly for imagewise exposing alayer of a solid solution copolymer that becomes crosslinked toinsoluble condition where light struck, the improvement according towhich the soluble copolymer has a molecular weight of about 5,000 to 1,500,000, is a copolymer of cyclopentadiene with indene oracenaphthylene, and contains about 30 to 70 mol percent ofcyclopentadiene.